Date of Award

Winter 12-18-2019

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Ecology and Environmental Sciences

Advisor

Allison Gardner

Second Committee Member

Anne Lichtenwalner

Third Committee Member

Alessio Mortelliti

Abstract

The northern range of the blacklegged tick (Ixodes scapularis) is expanding, and with it, the pathogens it vectors, including Borrelia burgdorferi, Anaplasma phagocytophilum, and Babesia microti. As the range of I. scapularis expands, understanding the impacts of land management practices on tick habitat and the wildlife communities that impact pathogen transmission may lead to vector-borne disease management. To determine the effects of timber harvesting on tick abundance and pathogen prevalence, for two consecutive years, we conducted an observational field study at five study sites in Hancock County, Maine, a hotspot of Lyme disease incidence in humans. Each study site consisted of two experimental units, one harvested (i.e., harvested within the past 5 years) and one control (i.e., not harvested in the past 20 years). In each experimental unit, we established a 3600 m2 grid and measured off-host tick densities, wildlife, and microclimate conditions. Each week, from June to July, tick dragging was conducted in control and harvested treatments to measure tick density and to collect I. scapularis nymphs for pathogen testing. In 2019, temperature and relative humidity were measured to assess microclimate differences between control and harvested treatments. Small mammals were trapped during July and August, the peak activity period of nymphal and larval I. scapularis, and to determine the number of feeding ticks, ticks were counted on the head and ears. Camera traps were deployed, corresponding with trapping sessions, to assess the activity of deer and predators of small mammals; the former is an important host for adult I. scapularis ticks and can contribute to long-distance dispersal of ticks, while the latter may impact disease transmission. Ixodes scapularis nymphs were tested for B. burgdorferi, as well as two less prevalent emerging tick-borne pathogens in Maine, Babesia microti and Anaplasma phagocytophilum. Overall, we found that timber harvesting decreased the presence of I. scapularis. This finding might be explained by higher maximum temperatures and maximum vapor pressure deficits in areas harvested for timber reducing I. scapularis questing activity and/or survival in harvested areas. There were significantly fewer individual small mammal captures per 100 trap nights in harvested treatments that could explain observed differences in blacklegged tick presence among treatments. We tested the effects of timber harvesting on other wildlife community metrics (i.e. small mammal species diversity, Peromyscus spp. population sizes, large mammal species diversity, deer activity and predator activity) in this study, and none of these appeared to be impacted by timber harvesting. In summary, this study reveals the potential to manage tick-borne disease exposure risk via forest management. In particular, management practices have the potential to reduce off-host tick survival and/or questing activity and therefore decrease the transmission of tick-borne diseases.

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